The present invention relates to chucks used to secure solid state devices during ultrasonic bonding of interconnecting wires to the devices.
Solid state devices are typically made by stamping a plurality of leads from a sheet of metal, the stamping comprising a so-called frame. Centrally disposed in the frame with respect to the frame leads is a pad on which a semiconductor device is mounted including integrated circuits and the like. These circuits are microminiature and require the bonding of interconnecting wires between the frame leads and the integrated circuit. The frame leads form leads which provide access to conventional external circuitry as known in the microminiature solid state device art.
In the ultrasonic bonding of the interconnecting wires to the frame leads and the integrated circuit mounted on the frame, fixturing is required to firmly secure these leads and the central frame pad including the circuitry mounted thereon during the ultrasonic bonding operation. Since the device frame is stamped from a thin sheet of metal typically about 0.010 inches thick, burrs formed during the stamping operation can be as great in size as the thickness of the material itself. The size and shape of the burrs may differ from frame to frame and from finger to finger as the die which forms the frames wears. In addition to burrs, the stamping operation can cause deformation of certain of the frame leads such that they are nonplanar with the remainder of the frame. In prior art chucks, when securing such frames for ultrasonic bonding, these burrs and distortions of the frame leads has resulted in some of the leads not being securely clamped. When an interconnecting wire is ultrasonically bonded to such a loosely clamped frame lead, the ultrasonic motions have a tendency to vibrate the poorly secured frame lead resulting in a poor ultrasonic bond. In the ultrasonic frame lead bonding industry, long standing attempts to reduce the burrs and distortions or minimize their deleterious effect on ultrasonic bonding have proved to be costly, ineffective and have met with little success.